SOIL DEGRADATION BY EROSION OF A TYPIC HAPLUDALF IN CENTRAL OHIO AND ITS REHABILITATION

Soil erosion and runoff were monitored from 1988 to 1990 on a Miamian soil (Typic Hapludalf) of 5-6 per cent slope using field runoff plots. Four treatments were studied: (i) disk-plough up and down the slope t o 0.3 m depth (DP); (ii) disk-plough up and down the slope followed by a protective netting (PN); (iii) uncultivated fallow without any vege tation followed by surface soil removal (R); (iv) uncultivated fallow with natural vegetation followed by ploughing (F). Mean annual runoff losses were 6, 114 and 128 mm, or 4, 20 and 18 per cent of the rainfal l, and mean annual soil losses were 1.2, 85.0 and 64.0 Mg ha(-1) in 19 88, 1989 and 1990, respectively. Mean runoff amounts were 26, 69, 116 and 118 mm and mean annual soil losses were 04, 23.2, 58.6 and 118 Mg ha(-1) for the F, PN, DP and R treatments, respectively. In comparison with DP, PN decreased annual runoff by 40.3 per cent and annual soil loss by 79.5 per cent. The high mean soil loss for the R treatment was due to erosion following soil removal. An additional 2920 Mg ha(-1) o f surface soil was removed from the R treatment in May 1990. The F tre atment reduced runoff by 78, 77 and 62 per cent and reduced soil loss by 99.7, 99.4 and 98.4 per cent compared with the R, DP and PN treatme nts, respectively. Mean losses of K, Ca, Mg and P were 1.3, 4, 1 and 0 .1 kg ha(-1), respectively for F, 3, 16, 5 and 0.3 kg ha(-1), respecti vely, for PN, 5, 31, 1 and 0.6 kg ha(-1), respectively, for DP, and 3, 32, 12 and 0.4 kg ha(-1), respectively, for R. Soil and nutrient loss es for each treatment were in the order R > DP > PN > F. The soil orga nic carbon (SOC) content was significantly affected by soil erosion an d management treatments, and ranged from 0.98 per cent for the R treat ment to 2.3 per cent for the F treatment. Soil surface removal for the R treatment in 1990 reduced water-stable aggregates (WSA) by 9.0 per cent, SOC by 0.6 per cent, and clay content of the uppermost 0-50 mm d epth by about 7.0 per cent. Mean total porosity (f(t)) ranged from 0.4 3 for the F to 0.52 for the DP treatment. Cumulative infiltration for 3 h ranged from 13 cm for R to 34 cm for PN, with corresponding infilt ration rates of 4cm h(-1) and 13 cm h(-1), respectively. Regardless of the treatment, there were also temporal changes in soil properties. I n comparison with 1988, measurements made in 1990 showed a significant decrease in WSA of 21.3 per cent, an increase in clay content of 2.8 per cent, and a decrease in SOC of 0.39 per cent. Runoff and soil loss es were significantly correlated with the mean weight diameter (MWD), SOC, bulk density (rho(b)) and available water capacity (AWC). Plant h eight measured 8 weeks after planting (WAP) for the R treatment was re duced by 33.3 per cent, 33.0 per cent and 29.0 per cent compared withh DP, PN and F, respectively. Nitrogen uptake by maize plants (Zea mays L.) 10 WAP for the R treatment was lower by 15 per cent, 8 per cent, and 6 per cent compared with the DP, PN and F treatments, respectively , while P uptake was lower by 33 per cent, 32 per cent and 29 per cent , respectively, compared with the same treatments. Grain yield was 9.7 8 Mg ha(-1) for PN, 9.76 Mg ha(-1) for DP, 8.64 Mg ha(-1) for F and 6. 60 Mg ha(-1) for R during the 1990 crop season. Grain yield was reduce d by about 32.4 per cent in the R treatment compared with the PN treat ment, representing a maize grain yield reduction of 158 kg ha(-1) for each centimeter of soil lost.